Question

早上好，

我第一次使用CoreData和Swift 2.2工作。此刻，我可以将对象添加到我的实体“Item”中，然后在按下“删除所有内容”按钮后删除所有项目。这是正确的，但当我删除所有对象然后重新启动我的应用程序时，我仍然在“删除所有内容”操作之前拥有相同的核心数据。

我如何删除核心数据对象：

// MARK: - Core Data stack

lazy var applicationDocumentsDirectory: NSURL = {
    // The directory the application uses to store the Core Data store file. This code uses a directory named "-.test" in the application's documents Application Support directory.
    let urls = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask)
    return urls[urls.count-1]
}()

lazy var managedObjectModel: NSManagedObjectModel = {
    // The managed object model for the application. This property is not optional. It is a fatal error for the application not to be able to find and load its model.
    let modelURL = NSBundle.mainBundle().URLForResource("wishlist", withExtension: "momd")!
    return NSManagedObjectModel(contentsOfURL: modelURL)!
}()

lazy var persistentStoreCoordinator: NSPersistentStoreCoordinator = {
    // The persistent store coordinator for the application. This implementation creates and returns a coordinator, having added the store for the application to it. This property is optional since there are legitimate error conditions that could cause the creation of the store to fail.
    // Create the coordinator and store
    let coordinator = NSPersistentStoreCoordinator(managedObjectModel: self.managedObjectModel)
    let url = self.applicationDocumentsDirectory.URLByAppendingPathComponent("SingleViewCoreData.sqlite")
    var failureReason = "There was an error creating or loading the application's saved data."
    do {
        try coordinator.addPersistentStoreWithType(NSSQLiteStoreType, configuration: nil, URL: url, options: nil)
    } catch {
        // Report any error we got.
        var dict = [String: AnyObject]()
        dict[NSLocalizedDescriptionKey] = "Failed to initialize the application's saved data"
        dict[NSLocalizedFailureReasonErrorKey] = failureReason

        dict[NSUnderlyingErrorKey] = error as NSError
        let wrappedError = NSError(domain: "YOUR_ERROR_DOMAIN", code: 9999, userInfo: dict)
        // Replace this with code to handle the error appropriately.
        // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
        NSLog("Unresolved error \(wrappedError), \(wrappedError.userInfo)")
        abort()
    }

    return coordinator
}()

lazy var managedObjectContext: NSManagedObjectContext = {
    // Returns the managed object context for the application (which is already bound to the persistent store coordinator for the application.) This property is optional since there are legitimate error conditions that could cause the creation of the context to fail.
    let coordinator = self.persistentStoreCoordinator
    var managedObjectContext = NSManagedObjectContext(concurrencyType: .MainQueueConcurrencyType)
    managedObjectContext.persistentStoreCoordinator = coordinator
    return managedObjectContext
}()

// MARK: - Core Data Saving support

func saveContext () {
    if managedObjectContext.hasChanges {
        do {
            try managedObjectContext.save()
        } catch {
            // Replace this implementation with code to handle the error appropriately.
            // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
            let nserror = error as NSError
            NSLog("Unresolved error \(nserror), \(nserror.userInfo)")
            abort()
        }
    }
}

它正在工作，因为当我按下按钮时，列表为空，但是当我重新启动应用程序时，它再次显示与按下“清除”按钮之前相同的项目。

这是我的 AppDelegate 与核心数据部分：

{{1}}

我对核心数据做错了什么？我该如何解决这个问题？

非常感谢，

问候。

Answer 1

在重新启动应用程序后重新获得这些对象的原因是，在执行所有删除操作后您没有保存NSManagedObjectContext，以便可以将这些更改保留到您正在使用的持久性存储中。

上下文就像一块虚拟板。将您在托管对象上的对象视为放在桌子上玩具的玩具。您可以移动它们，打破它们，将它们移出桌面，然后带入新玩具。该表是您的托管对象上下文，您可以在准备好时保存其状态。保存托管对象上下文的状态时，此保存操作将传递给上下文所连接的持久性存储协调器。然后，持久性存储协调器将信息存储到持久性存储中，然后存储到磁盘。

func deleteAllData(entity: String) {

let appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate
let managedContext = appDelegate.managedObjectContext
let fetchRequest = NSFetchRequest(entityName: entity)
fetchRequest.returnsObjectsAsFaults = false

do
  {
    let results = try managedContext.executeFetchRequest(fetchRequest)
    for managedObject in results
    {
        let managedObjectData:NSManagedObject = managedObject as! NSManagedObject
        managedContext.deleteObject(managedObjectData)
        print("Deleted")
    }

  } catch let error as NSError {
    print(error)
  }
  appDelegate.saveContext()
}

为了获得性能优势，您应该查看NSBatchDeleteRequest。

删除它并重新启动我的应用程序后，Core Data是持久的

1 个答案: